The invention relates to a modulating valve for controlling the flow of a heating or cooling liquid. More particularly, the invention is a microprocessor driven controller for controlling the position of a valve plug member in a modulating valve.
In many present heating and cooling systems, a pneumatically controlled modulating valve is used to regulate the flow of the heating or cooling liquid throughout the system. These modulating valves are controlled by a source of varying air pressure supplied to a diaphragm in the modulating valve to control the position of the valve plug member within the valve body. By changing the amount of air pressure applied to the modulating valve, the position of the valve plug can be controlled, thus regulating the flow of heating or cooling liquid through the system. Although this method of controlling the flow of liquid through a valve has been effective for many years, it requires a source of pneumatic pressure to be piped throughout a building in order to provide control for the various modulating valves.
In many new building constructions and in the retrofitting of old buildings, it is desired to provide a main electronic controller which controls the environment of the enclosed space. When modifying an existing building that has pneumatically controlled modulating valves, it is desirable to replace the pneumatic valve with an electronically controlled modulating valve such that the valve can be controlled by the main controller.
Currently, many electronically controlled modulating valves include a potentiometer connected to the valve stem, such that the movement of the valve stem between the open and closed position rotates the potentiometer, thereby varying the resistance. The potentiometer is coupled to a control circuit, such that the position of the valve stem can be monitored by measuring the changing resistance. The described modulating valve has several drawbacks. For instance, the potentiometer included in the valve must be a very accurate device and must be factory pre-set, since the range of resistance of the potentiometer between the completely open and completely closed valve position must be precisely known. Presetting the potentiometer adds to both the cost and production time of a modulating valve. In addition to the cost constraints, the mechanical feedback provided by the rotating potentiometer suffers from the limited life of the potentiometer and reliability problems resulting from normal wear during continuous usage.
Many modulating valves include a clutch assembly and return spring which allows the valve to return to a specific state, either completely open or completely closed, upon power or pressure loss to the valve. In electronically controlled valves, the clutch assembly is operated by an electric solenoid which must be activated to engage a series of gears, thereby allowing an electric motor in the valve to move the valve plug member. Upon power loss, it is desirable that the solenoid disengage the gear assembly, thereby allowing the return spring to either completely open or completely close the valve depending upon the system requirements. Typically, to operate the solenoid clutch, additional circuitry must be included in the valve controller, such that the solenoid can be deactivated upon power loss. This additional circuitry increases the cost and design complexity of the modulating valve.
It is therefore an object of the invention to provide a microcontroller based electronic controller to accurately operate a modulating valve. It is another object of the invention to provide an electronic controller which monitors the position of the valve stem without the use of a factory pre-set potentiometer. It is another feature of the invention to provide an electronic controller which can calibrate itself to determine the valve stroke from a completely open to a completely closed position and position the valve stem accurately based on an input signal. It is another feature of the invention to provide an electronic controller which is able to select from a variety of input ranges, such that the modulating valve may be used with a variety of external temperature controllers.